ref: fb7dd4b3a868cb8987049c95bb32e6425a73c8b9
dir: /os/boot/pc/l.s/
#include "x16.h" #include "mem.h" #define WRMSR BYTE $0x0F; BYTE $0x30 /* WRMSR, argument in AX/DX (lo/hi) */ #define RDTSC BYTE $0x0F; BYTE $0x31 /* RDTSC, result in AX/DX (lo/hi) */ #define RDMSR BYTE $0x0F; BYTE $0x32 /* RDMSR, result in AX/DX (lo/hi) */ #ifdef PXE #define PDB 0x90000 /* temporary page tables (24KB) */ #else #define PDB 0x08000 #endif PXE #define NoScreenBlank 1 /*#define ResetDiscs 1*/ TEXT origin(SB), $0 /* * This part of l.s is used only in the boot kernel. * It assumes that we are in real address mode, i.e., * that we look like an 8086. * * Make sure the segments are reasonable. * If we were started directly from the BIOS * (i.e. no MS-DOS) then DS may not be * right. */ MOVW CS, AX MOVW AX, DS #ifdef NoScreenBlank /* * Get the current video mode. If it isn't mode 3, * set text mode 3. * Well, no. Windows95 won't co-operate here so we have * to explicitly set mode 3. */ XORL AX, AX MOVB $0x0F, AH INT $0x10 /* get current video mode in AL */ CMPB AL, $03 JEQ sayhello #endif /* NoScreenBlank */ XORL AX, AX MOVB $0x03, AL INT $0x10 /* set video mode in AL */ sayhello: LWI(hello(SB), rSI) CALL16(biosputs(SB)) #ifdef ResetDiscs XORL AX, AX /* reset disc system */ XORL DX, DX MOVB $0x80, DL INT $0x13 #endif /* ResetDiscs */ #ifdef DOTCOM /* * relocate everything to a half meg and jump there * - looks weird because it is being assembled by a 32 bit * assembler for a 16 bit world * * only b.com does this - not 9load */ MOVL $0,BX INCL BX SHLL $15,BX MOVL BX,CX MOVW BX,ES MOVL $0,SI MOVL SI,DI CLD REP MOVSL /* * Jump to the copied image; * fix up the DS for the new location. */ FARJUMP16(0x8000, _start8000(SB)) TEXT _start8000(SB), $0 MFSR(rCS, rAX) /* fix up DS, ES (0x8000) */ MTSR(rAX, rDS) MTSR(rAX, rES) /* * If we are already in protected mode, have to get back * to real mode before trying any privileged operations * (like going into protected mode...). * Try to reset with a restart vector. */ MFCR(rCR0, rAX) /* are we in protected mode? */ ANDI(0x0001, rAX) JEQ _real CLR(rBX) MTSR(rBX, rES) LWI(0x0467, rBX) /* reset entry point */ LWI(_start8000(SB), rAX) /* offset within segment */ BYTE $0x26 BYTE $0x89 BYTE $0x07 /* MOVW AX, ES:[BX] */ LBI(0x69, rBL) MFSR(rCS, rAX) /* segment */ BYTE $0x26 BYTE $0x89 BYTE $0x07 /* MOVW AX, ES:[BX] */ CLR(rDX) OUTPORTB(0x70, 0x8F) OUTPORTB(0x71, 0x0A) FARJUMP16(0xFFFF, 0x0000) /* reset */ #endif /* DOTCOM */ _real: /* * do things that need to be done in real mode. * the results get written to CONFADDR (0x1200) * in a series of <4-byte-magic-number><block-of-data> * the data length is dependent on the magic number. * * this gets parsed by conf.c:/^readlsconf * * N.B. CALL16 kills rDI, so we can't call anything. */ LWI(0x0000, rAX) MTSR(rAX, rES) LWI(0x1200, rDI) /* * turn off interrupts */ CLI /* * detect APM1.2 bios support */ /* save DI */ SW(rDI, rock(SB)) /* disconnect anyone else */ LWI(0x5304, rAX) LWI(0x0000, rBX) INT $0x15 /* connect */ CLC LWI(0x5303, rAX) LWI(0x0000, rBX) INT $0x15 CLI /* apm put interrupts back? */ JC noapm OPSIZE; PUSHR(rSI) OPSIZE; PUSHR(rBX) PUSHR(rDI) PUSHR(rDX) PUSHR(rCX) PUSHR(rAX) /* put DI, ES back */ LW(rock(SB), rDI) LWI(0x0000, rAX) MTSR(rAX, rES) /* * write APM data. first four bytes are APM\0. */ LWI(0x5041, rAX) STOSW LWI(0x004d, rAX) STOSW LWI(8, rCX) apmmove: POPR(rAX) STOSW LOOP apmmove noapm: /* * end of real mode hacks: write terminator, put ES back. */ LWI(0x0000, rAX) STOSW STOSW MFSR(rCS, rAX) /* fix up ES (0x8000) */ MTSR(rAX, rES) /* * goto protected mode */ /* MOVL tgdtptr(SB),GDTR /**/ BYTE $0x0f BYTE $0x01 BYTE $0x16 WORD $tgdtptr(SB) LWI(1, rAX) /* MOV AX,MSW */ BYTE $0x0F; BYTE $0x01; BYTE $0xF0 /* * clear prefetch queue (weird code to avoid optimizations) */ /* JMP .+2 */ BYTE $0xEB BYTE $0x00 /* * set all segs */ /* MOVW $SELECTOR(1, SELGDT, 0),AX /**/ BYTE $0xc7 BYTE $0xc0 WORD $SELECTOR(1, SELGDT, 0) MOVW AX,DS MOVW AX,SS MOVW AX,ES MOVW AX,FS MOVW AX,GS /* JMPFAR SELECTOR(2, SELGDT, 0):$mode32bit(SB) /**/ BYTE $0x66 BYTE $0xEA LONG $mode32bit-KZERO(SB) WORD $SELECTOR(2, SELGDT, 0) TEXT mode32bit(SB),$0 /* * make a bottom level page table page that maps the first * 16 meg of physical memory */ MOVL $PDB, DI /* clear 6 pages for the tables etc. */ XORL AX, AX MOVL $(6*BY2PG), CX SHRL $2, CX CLD REP; STOSL MOVL $PDB, AX /* phys addr of temporary page table */ MOVL $(4*1024),CX /* pte's per page */ MOVL $((((4*1024)-1)<<PGSHIFT)|PTEVALID|PTEKERNEL|PTEWRITE),BX setpte: MOVL BX,-4(AX)(CX*4) SUBL $(1<<PGSHIFT),BX LOOP setpte /* * make a top level page table page that maps the first * 16 meg of memory to 0 thru 16meg and to KZERO thru KZERO+16meg */ MOVL AX,BX ADDL $(4*BY2PG),AX ADDL $(PTEVALID|PTEKERNEL|PTEWRITE),BX MOVL BX,0(AX) MOVL BX,((((KZERO>>1)&0x7FFFFFFF)>>(2*PGSHIFT-1-4))+0)(AX) ADDL $BY2PG,BX MOVL BX,4(AX) MOVL BX,((((KZERO>>1)&0x7FFFFFFF)>>(2*PGSHIFT-1-4))+4)(AX) ADDL $BY2PG,BX MOVL BX,8(AX) MOVL BX,((((KZERO>>1)&0x7FFFFFFF)>>(2*PGSHIFT-1-4))+8)(AX) ADDL $BY2PG,BX MOVL BX,12(AX) MOVL BX,((((KZERO>>1)&0x7FFFFFFF)>>(2*PGSHIFT-1-4))+12)(AX) /* * point processor to top level page & turn on paging * * this produces the apparently harmless "VMX|F(125):468 Dis 0x0:0x0" * message in the VMware log. */ MOVL AX,CR3 MOVL CR0,AX ORL $0X80000000,AX MOVL AX,CR0 /* * use a jump to an absolute location to get the PC into * KZERO. */ LEAL tokzero(SB),AX JMP* AX /* * When we load 9load from DOS, the bootstrap jumps * to the instruction right after `JUMP', which gets * us into kzero. * * The name prevents it from being optimized away. */ TEXT jumplabel(SB), $0 BYTE $'J'; BYTE $'U'; BYTE $'M'; BYTE $'P' LEAL tokzero(SB),AX JMP* AX TEXT tokzero(SB),$0 /* * Clear BSS */ LEAL edata(SB),SI MOVL SI,DI ADDL $4,DI MOVL $0,AX MOVL AX,(SI) LEAL end(SB),CX SUBL DI,CX SHRL $2,CX CLD REP MOVSL /* * stack and mach */ MOVL $mach0(SB),SP MOVL SP,m(SB) MOVL $0,0(SP) ADDL $(MACHSIZE-4),SP /* start stack above machine struct */ CALL main(SB) loop: JMP loop GLOBL mach0+0(SB), $MACHSIZE GLOBL m(SB), $4 /* * gdt to get us to 32-bit/segmented/unpaged mode */ TEXT tgdt(SB),$0 /* null descriptor */ LONG $0 LONG $0 /* data segment descriptor for 4 gigabytes (PL 0) */ LONG $(0xFFFF) LONG $(SEGG|SEGB|(0xF<<16)|SEGP|SEGPL(0)|SEGDATA|SEGW) /* exec segment descriptor for 4 gigabytes (PL 0) */ LONG $(0xFFFF) LONG $(SEGG|SEGD|(0xF<<16)|SEGP|SEGPL(0)|SEGEXEC|SEGR) /* exec segment descriptor for 4 gigabytes (PL 0) 16-bit */ LONG $(0xFFFF) LONG $(SEGG|(0xF<<16)|SEGP|SEGPL(0)|SEGEXEC|SEGR) /* * pointer to initial gdt */ TEXT tgdtptr(SB),$0 WORD $(4*8) LONG $tgdt-KZERO(SB) /* * Output a string to the display. * String argument is in rSI. */ TEXT biosputs(SB), $0 PUSHA CLR(rBX) _BIOSputs: LODSB ORB(rAL, rAL) JEQ _BIOSputsret LBI(0x0E, rAH) BIOSCALL(0x10) JMP _BIOSputs _BIOSputsret: POPA RET /* * input a byte */ TEXT inb(SB),$0 MOVL p+0(FP),DX XORL AX,AX INB RET /* * input a short from a port */ TEXT ins(SB), $0 MOVL p+0(FP), DX XORL AX, AX OPSIZE; INL RET /* * input a long from a port */ TEXT inl(SB), $0 MOVL p+0(FP), DX XORL AX, AX INL RET /* * output a byte */ TEXT outb(SB),$0 MOVL p+0(FP),DX MOVL b+4(FP),AX OUTB RET /* * output a short to a port */ TEXT outs(SB), $0 MOVL p+0(FP), DX MOVL s+4(FP), AX OPSIZE; OUTL RET /* * output a long to a port */ TEXT outl(SB), $0 MOVL p+0(FP), DX MOVL s+4(FP), AX OUTL RET /* * input a string of bytes from a port */ TEXT insb(SB),$0 MOVL p+0(FP),DX MOVL a+4(FP),DI MOVL c+8(FP),CX CLD; REP; INSB RET /* * input a string of shorts from a port */ TEXT inss(SB),$0 MOVL p+0(FP),DX MOVL a+4(FP),DI MOVL c+8(FP),CX CLD REP; OPSIZE; INSL RET /* * output a string of bytes to a port */ TEXT outsb(SB),$0 MOVL p+0(FP),DX MOVL a+4(FP),SI MOVL c+8(FP),CX CLD; REP; OUTSB RET /* * output a string of shorts to a port */ TEXT outss(SB),$0 MOVL p+0(FP),DX MOVL a+4(FP),SI MOVL c+8(FP),CX CLD REP; OPSIZE; OUTSL RET /* * input a string of longs from a port */ TEXT insl(SB),$0 MOVL p+0(FP),DX MOVL a+4(FP),DI MOVL c+8(FP),CX CLD; REP; INSL RET /* * output a string of longs to a port */ TEXT outsl(SB),$0 MOVL p+0(FP),DX MOVL a+4(FP),SI MOVL c+8(FP),CX CLD; REP; OUTSL RET /* * routines to load/read various system registers */ GLOBL idtptr(SB),$6 TEXT putidt(SB),$0 /* interrupt descriptor table */ MOVL t+0(FP),AX MOVL AX,idtptr+2(SB) MOVL l+4(FP),AX MOVW AX,idtptr(SB) MOVL idtptr(SB),IDTR RET TEXT putcr3(SB),$0 /* top level page table pointer */ MOVL t+0(FP),AX MOVL AX,CR3 RET TEXT getcr0(SB),$0 /* coprocessor bits */ MOVL CR0,AX RET TEXT getcr2(SB),$0 /* fault address */ MOVL CR2,AX RET TEXT getcr3(SB),$0 /* page directory base */ MOVL CR3,AX RET TEXT getcr4(SB), $0 /* CR4 - extensions */ MOVL CR4, AX RET TEXT _cycles(SB), $0 /* time stamp counter */ RDTSC MOVL vlong+0(FP), CX /* &vlong */ MOVL AX, 0(CX) /* lo */ MOVL DX, 4(CX) /* hi */ RET TEXT rdmsr(SB), $0 /* model-specific register */ MOVL index+0(FP), CX RDMSR MOVL vlong+4(FP), CX /* &vlong */ MOVL AX, 0(CX) /* lo */ MOVL DX, 4(CX) /* hi */ RET TEXT wrmsr(SB), $0 MOVL index+0(FP), CX MOVL lo+4(FP), AX MOVL hi+8(FP), DX WRMSR RET TEXT mb386(SB), $0 POPL AX /* return PC */ PUSHFL PUSHL CS PUSHL AX IRETL /* * special traps */ TEXT intr0(SB),$0 PUSHL $0 PUSHL $0 JMP intrcommon TEXT intr1(SB),$0 PUSHL $0 PUSHL $1 JMP intrcommon TEXT intr2(SB),$0 PUSHL $0 PUSHL $2 JMP intrcommon TEXT intr3(SB),$0 PUSHL $0 PUSHL $3 JMP intrcommon TEXT intr4(SB),$0 PUSHL $0 PUSHL $4 JMP intrcommon TEXT intr5(SB),$0 PUSHL $0 PUSHL $5 JMP intrcommon TEXT intr6(SB),$0 PUSHL $0 PUSHL $6 JMP intrcommon TEXT intr7(SB),$0 PUSHL $0 PUSHL $7 JMP intrcommon TEXT intr8(SB),$0 PUSHL $8 JMP intrcommon TEXT intr9(SB),$0 PUSHL $0 PUSHL $9 JMP intrcommon TEXT intr10(SB),$0 PUSHL $10 JMP intrcommon TEXT intr11(SB),$0 PUSHL $11 JMP intrcommon TEXT intr12(SB),$0 PUSHL $12 JMP intrcommon TEXT intr13(SB),$0 PUSHL $13 JMP intrcommon TEXT intr14(SB),$0 PUSHL $14 JMP intrcommon TEXT intr15(SB),$0 PUSHL $0 PUSHL $15 JMP intrcommon TEXT intr16(SB),$0 PUSHL $0 PUSHL $16 JMP intrcommon TEXT intr24(SB),$0 PUSHL $0 PUSHL $24 JMP intrcommon TEXT intr25(SB),$0 PUSHL $0 PUSHL $25 JMP intrcommon TEXT intr26(SB),$0 PUSHL $0 PUSHL $26 JMP intrcommon TEXT intr27(SB),$0 PUSHL $0 PUSHL $27 JMP intrcommon TEXT intr28(SB),$0 PUSHL $0 PUSHL $28 JMP intrcommon TEXT intr29(SB),$0 PUSHL $0 PUSHL $29 JMP intrcommon TEXT intr30(SB),$0 PUSHL $0 PUSHL $30 JMP intrcommon TEXT intr31(SB),$0 PUSHL $0 PUSHL $31 JMP intrcommon TEXT intr32(SB),$0 PUSHL $0 PUSHL $32 JMP intrcommon TEXT intr33(SB),$0 PUSHL $0 PUSHL $33 JMP intrcommon TEXT intr34(SB),$0 PUSHL $0 PUSHL $34 JMP intrcommon TEXT intr35(SB),$0 PUSHL $0 PUSHL $35 JMP intrcommon TEXT intr36(SB),$0 PUSHL $0 PUSHL $36 JMP intrcommon TEXT intr37(SB),$0 PUSHL $0 PUSHL $37 JMP intrcommon TEXT intr38(SB),$0 PUSHL $0 PUSHL $38 JMP intrcommon TEXT intr39(SB),$0 PUSHL $0 PUSHL $39 JMP intrcommon TEXT intr64(SB),$0 PUSHL $0 PUSHL $64 JMP intrcommon TEXT intrbad(SB),$0 PUSHL $0 PUSHL $0x1ff JMP intrcommon intrcommon: PUSHL DS PUSHL ES PUSHL FS PUSHL GS PUSHAL MOVL $(KDSEL),AX MOVW AX,DS MOVW AX,ES LEAL 0(SP),AX PUSHL AX CALL trap(SB) POPL AX POPAL POPL GS POPL FS POPL ES POPL DS ADDL $8,SP /* error code and trap type */ IRETL /* * interrupt level is interrupts on or off */ TEXT spllo(SB),$0 PUSHFL POPL AX STI RET TEXT splhi(SB),$0 PUSHFL POPL AX CLI RET TEXT splx(SB),$0 MOVL s+0(FP),AX PUSHL AX POPFL RET /* * do nothing whatsoever till interrupt happens */ TEXT idle(SB),$0 HLT RET /* * Try to determine the CPU type which requires fiddling with EFLAGS. * If the Id bit can be toggled then the CPUID instruciton can be used * to determine CPU identity and features. First have to check if it's * a 386 (Ac bit can't be set). If it's not a 386 and the Id bit can't be * toggled then it's an older 486 of some kind. * * cpuid(id[], &ax, &dx); */ #define CPUID BYTE $0x0F; BYTE $0xA2 /* CPUID, argument in AX */ TEXT cpuid(SB), $0 MOVL $0x240000, AX PUSHL AX POPFL /* set Id|Ac */ PUSHFL POPL BX /* retrieve value */ MOVL $0, AX PUSHL AX POPFL /* clear Id|Ac, EFLAGS initialised */ PUSHFL POPL AX /* retrieve value */ XORL BX, AX TESTL $0x040000, AX /* Ac */ JZ _cpu386 /* can't set this bit on 386 */ TESTL $0x200000, AX /* Id */ JZ _cpu486 /* can't toggle this bit on some 486 */ MOVL $0, AX CPUID MOVL id+0(FP), BP MOVL BX, 0(BP) /* "Genu" "Auth" "Cyri" */ MOVL DX, 4(BP) /* "ineI" "enti" "xIns" */ MOVL CX, 8(BP) /* "ntel" "cAMD" "tead" */ MOVL $1, AX CPUID JMP _cpuid _cpu486: MOVL $0x400, AX MOVL $0, DX JMP _cpuid _cpu386: MOVL $0x300, AX MOVL $0, DX _cpuid: MOVL ax+4(FP), BP MOVL AX, 0(BP) MOVL dx+8(FP), BP MOVL DX, 0(BP) RET /* * basic timing loop to determine CPU frequency */ TEXT aamloop(SB),$0 MOVL c+0(FP),CX aaml1: AAM LOOP aaml1 RET TEXT hello(SB), $0 BYTE $'P'; BYTE $'l'; BYTE $'a'; BYTE $'n'; BYTE $' '; BYTE $'9'; BYTE $' '; BYTE $'f'; BYTE $'r'; BYTE $'o'; BYTE $'m'; BYTE $' '; BYTE $'B'; BYTE $'e'; BYTE $'l'; BYTE $'l'; BYTE $' '; BYTE $'L'; BYTE $'a'; BYTE $'b'; BYTE $'s'; #ifdef PXE BYTE $' '; BYTE $'b'; BYTE $'y'; BYTE $' '; BYTE $'P'; BYTE $'X'; BYTE $'E'; #endif BYTE $'\r'; BYTE $'\n'; BYTE $'\z'; TEXT rock(SB), $0 BYTE $0; BYTE $0; BYTE $0; BYTE $0; GLOBL pxe(SB), $4 #ifdef PXE DATA pxe+0(SB)/4, $1 #else DATA pxe+0(SB)/4, $0 #endif /* PXE */ /* * Save registers. */ TEXT saveregs(SB), $0 /* appease 8l */ SUBL $32, SP POPL AX POPL AX POPL AX POPL AX POPL AX POPL AX POPL AX POPL AX PUSHL AX PUSHL BX PUSHL CX PUSHL DX PUSHL BP PUSHL DI PUSHL SI PUSHFL XCHGL 32(SP), AX /* swap return PC and saved flags */ XCHGL 0(SP), AX XCHGL 32(SP), AX RET TEXT restoreregs(SB), $0 /* appease 8l */ PUSHL AX PUSHL AX PUSHL AX PUSHL AX PUSHL AX PUSHL AX PUSHL AX PUSHL AX ADDL $32, SP XCHGL 32(SP), AX /* swap return PC and saved flags */ XCHGL 0(SP), AX XCHGL 32(SP), AX POPFL POPL SI POPL DI POPL BP POPL DX POPL CX POPL BX POPL AX RET /* * Assumed to be in protected mode at time of call. * Switch to real mode, execute an interrupt, and * then switch back to protected mode. * * Assumes: * * - no device interrupts are going to come in * - 0-16MB is identity mapped in page tables * - can use code segment 0x1000 in real mode * to get at l.s code */ TEXT realmodeidtptr(SB), $0 WORD $(4*256-1) LONG $0 TEXT realmode0(SB), $0 CALL saveregs(SB) /* switch to low code address */ LEAL physcode-KZERO(SB), AX JMP *AX TEXT physcode(SB), $0 /* switch to low stack */ MOVL SP, AX MOVL $0x7C00, SP PUSHL AX /* load IDT with real-mode version; GDT already fine */ MOVL realmodeidtptr(SB), IDTR /* edit INT $0x00 instruction below */ MOVL realmodeintr(SB), AX MOVB AX, realmodeintrinst+1(SB) /* disable paging */ MOVL CR0, AX ANDL $0x7FFFFFFF, AX MOVL AX, CR0 /* JMP .+2 to clear prefetch queue*/ BYTE $0xEB; BYTE $0x00 /* jump to 16-bit code segment */ /* JMPFAR SELECTOR(3, SELGDT, 0):$again16bit(SB) /**/ BYTE $0xEA LONG $again16bit-KZERO(SB) WORD $SELECTOR(3, SELGDT, 0) TEXT again16bit(SB), $0 /* * Now in 16-bit compatibility mode. * These are 32-bit instructions being interpreted * as 16-bit instructions. I'm being lazy and * not using the macros because I know when * the 16- and 32-bit instructions look the same * or close enough. */ /* disable protected mode and jump to real mode cs */ OPSIZE; MOVL CR0, AX OPSIZE; XORL BX, BX OPSIZE; INCL BX OPSIZE; XORL BX, AX OPSIZE; MOVL AX, CR0 /* JMPFAR 0x1000:now16real */ BYTE $0xEA WORD $now16real-KZERO(SB) WORD $0x1000 TEXT now16real(SB), $0 /* copy the registers for the bios call */ LWI(0x1000, rAX) MOVW AX,SS LWI(realmoderegs(SB), rBP) /* offsets are in Ureg */ LXW(44, xBP, rAX) MOVW AX, DS LXW(40, xBP, rAX) MOVW AX, ES OPSIZE; LXW(0, xBP, rDI) OPSIZE; LXW(4, xBP, rSI) OPSIZE; LXW(16, xBP, rBX) OPSIZE; LXW(20, xBP, rDX) OPSIZE; LXW(24, xBP, rCX) OPSIZE; LXW(28, xBP, rAX) CLC TEXT realmodeintrinst(SB), $0 INT $0x00 /* save the registers after the call */ LWI(0x7bfc, rSP) OPSIZE; PUSHFL OPSIZE; PUSHL AX LWI(0x1000, rAX) MOVW AX,SS LWI(realmoderegs(SB), rBP) OPSIZE; SXW(rDI, 0, xBP) OPSIZE; SXW(rSI, 4, xBP) OPSIZE; SXW(rBX, 16, xBP) OPSIZE; SXW(rDX, 20, xBP) OPSIZE; SXW(rCX, 24, xBP) OPSIZE; POPL AX OPSIZE; SXW(rAX, 28, xBP) MOVW DS, AX OPSIZE; SXW(rAX, 44, xBP) MOVW ES, AX OPSIZE; SXW(rAX, 40, xBP) OPSIZE; POPL AX OPSIZE; SXW(rAX, 64, xBP) /* flags */ /* re-enter protected mode and jump to 32-bit code */ OPSIZE; MOVL $1, AX OPSIZE; MOVL AX, CR0 /* JMPFAR SELECTOR(2, SELGDT, 0):$again32bit(SB) /**/ OPSIZE BYTE $0xEA LONG $again32bit-KZERO(SB) WORD $SELECTOR(2, SELGDT, 0) TEXT again32bit(SB), $0 MOVW $SELECTOR(1, SELGDT, 0),AX MOVW AX,DS MOVW AX,SS MOVW AX,ES MOVW AX,FS MOVW AX,GS /* enable paging and jump to kzero-address code */ MOVL CR0, AX ORL $0x80000000, AX MOVL AX, CR0 LEAL again32kzero(SB), AX JMP* AX TEXT again32kzero(SB), $0 /* breathe a sigh of relief - back in 32-bit protected mode */ /* switch to old stack */ PUSHL AX /* match popl below for 8l */ MOVL $0x7BFC, SP POPL SP /* restore idt */ MOVL idtptr(SB),IDTR CALL restoreregs(SB) RET TEXT realmoderegs(SB), $0 LONG $0; LONG $0; LONG $0; LONG $0 LONG $0; LONG $0; LONG $0; LONG $0 LONG $0; LONG $0; LONG $0; LONG $0 LONG $0; LONG $0; LONG $0; LONG $0 LONG $0; LONG $0; LONG $0; LONG $0 TEXT realmodeintr(SB), $0 LONG $0